Any words on how to get loads and loads of wars in the world gen? I'm willing to mod the entities, if that's what it takes. Sadly making all the civs live in cities in the plains didn't seem to work =/
Add more races, even if they're copies, with unique [ENTITY:NAME] entries, in entity_default.txt in the /raws/objects folder. You can take [ENTITY:EVIL] for example (goblins), and make 6 copies of it, [ENTITY:SORTAEVIL], [ENTITY:VERYEVIL], etc as many as you want.
I removed all the races except dwarves and goblins and made 6 copies of the goblin race. I got 6 unqiue civs, all of which show up on the civilization interaction screen, both prior to embark, and after. However, to be at war with them, you'd probably have to make your dwarves babysnatchers to create offenses as time passes. I haven't tried that.
So far, I've only ever seen one WAR tag show up on a given embark screen at a time, regardless of how many civs are there. Even with 6 goblin civs, only one will be at WAR in a given world tile, even if the next one, in the adjacent embark, is a different civ at WAR. Of course, this is only in my experience, so things could be different for anyone else. And perhaps it's possible to be at WAR with all of them, if you turn dwarves into babysnatchers.
It may be necessary to create/copy Goblins (in creature_standard.txt) and create unique races for each unique civ, as well. Not difficult, but I haven't tested it yet. That may allow for multiple race-wars simultaneously.
For the moment, I'm testing this 6 goblin civ version to see if I can get multiple sieges per season/year with >100 goblins in each siege.